1. Technical Field
This technology relates to ballistic resistant composite articles having improved backface deformation resistance as well as superior ballistic penetration resistance.
2. Description of the Related Art
Ballistic resistant articles such as bullet resistant vests, helmets, vehicle panels and structural members of military equipment are typically made from composite armor comprising high strength fibers. High strength fibers conventionally used to fabricate composite armor include polyethylene fibers, aramid fibers such as poly(phenylenediamine terephthalamide), graphite fibers, nylon fibers, glass fibers and the like. For some applications, the fibers are formed into woven or knitted fabrics. For other applications, the fibers are coated with a polymeric binder material and formed into non-woven fabrics.
Various ballistic resistant constructions are known that are useful for the formation of hard or soft armor articles such as helmets, panels and vests. For example, U.S. Pat. Nos. 4,403,012, 4,457,985, 4,613,535, 4,623,574, 4,650,710, 4,737,402, 4,748,064, 5,552,208, 5,587,230, 6,642,159, 6,841,492, 6,846,758, all of which are incorporated herein by reference, describe ballistic resistant composites which include high strength fibers made from materials such as extended chain ultra-high molecular weight polyethylene. These composites display varying degrees of ballistic resistance to high speed projectiles such as bullets, shells, shrapnel and the like.
The two primary measures of anti-ballistic performance of composite armor are ballistic penetration resistance and blunt trauma (“trauma”) resistance. A common characterization of ballistic penetration resistance is the V50 velocity, which is the experimentally derived, statistically calculated impact velocity at which a projectile is expected to completely penetrate armor 50% of the time and be completely stopped by the armor 50% of the time. For composites of equal areal density (i.e. the weight of the composite armor divided by the surface area) the higher the V50 the better the penetration resistance of the composite.
Whether or not a high speed projectile penetrates armor, when the projectile engages the armor the impact also deflects the body armor at the area of impact, potentially causing significant non-penetrating, blunt trauma injuries. The measure of the depth of deflection of body armor due to a bullet impact is known as backface signature (“BFS”), also known in the art as backface deformation or trauma signature. Potentially resulting blunt trauma injuries may be as deadly to an individual as if the bullet had fully penetrated the armor and entered the body. This is especially consequential in the context of helmet armor, where the transient protrusion caused by a stopped bullet can still cross the plane of the skull underneath the helmet and cause debilitating or fatal brain damage. Accordingly, there is a need in the art for ballistic resistant composites having both superior V50 ballistic performance as well as low backface signature.
It is known that the V50 ballistic performance of fibrous composite armor is directly related to the strength of the constituent fibers of the composite. Increases in fiber strength properties such as tenacity and tensile modulus are known to correlate with an increase in V50 velocity. However, a corresponding improvement in backface signature reduction with increased fiber strength properties has not been similarly recognized. Typically, backface deformation reduction has been addressed by coupling high V50 fabric composites with energy absorbing backing materials, such as energy mitigating foams or honeycomb materials that absorb impact energy rather than transmitting it to the user. However, such backing materials typically add excessive bulk and/or weight to the armor articles and thus are not well suited for use in body armor applications.
In view of these problems, there is an ongoing need in the art for improved armor solutions that have both superior ballistic penetration resistance as well as low backface signature performance. The invention provides a solution to this need.